2Design of O-Ring SealsPrimary Source of information
3Why O-Rings? Can be used for static and dynamic applications Compact – need very little space - light weightEasy to incorporate into designDo not require high accuracySimple design rulesEasy to install or removeEasy to serviceAvailable in many standard sizes, materials
4Why O-Rings? Wide range of operating temperatures Wide range of operating pressuresGood durability and abrasion resistanceMany O-ring materials for a wide range of chemicalsTheir failure or deterioration is gradualInexpensive
5Limitations of O-rings Temperature (typically between -40 and 400 degrees F)Rotary speeds ( not to exceeding 1500 feet per minute)For a 2 inch shaft, it is 3000 rpmVulnerable to sharp edgesRequire small clearances
7Popular O-ring materials Nitrile (Buna-N)Variety of trade namesCopolymer of butadiene and acrylonitrileMost widely used and economical elastomerTemperature Range: Standard Compound: -40° to +257°FHardness (Shore A): 40 to 90
8Popular O-ring materials Nitrile (Buna-N) Excellent resistance topetroleum-based oils and fuelssilicone greaseshydraulic fluidswater and alcoholHigh tensile strengthHigh abrasion resistance
9Popular O-ring materials Nitrile (Buna-N) ApplicationsOil resistant applicationsLow temperature usesOff-road equipmentAutomotive, marine, aircraft fuel systems
10Other O-ring Materials Viton® / FKM: Fluorocarbon (Viton®) exceptional resistance to chemicals, oils, temperature extremes (-13°F to +446°F), low compression set. Applications include: aircraft engines, automotive fuel handling systems, and chemical processing industries.Ethylene-Propylene / EPDM: EPDM has excellent resistance to heat, water and steam, alkali, mild acidic and solvents, ozone, and sunlight with a temperature range of (-40ºF to +275ºF); but it is not recommended for gasoline, petroleum oil and grease, and hydrocarbon environments.
11Other O-ring Materials Fluorosilicone / FVMQ: Fluorosilicone (-75º to +400ºF) combines the good high and low temperature stability of silicones with the fuel, oil, and solvent resistance of fluorocarbons. FVMQ is used for aerospace fuel systems, auto fuel emission control systems. However, due to relatively low tear strength, high friction and limited abrasion resistance of these materials, they are generally not used in dynamic applications.
12Other O-ring Materials Silicone / VMQ: Superior as static seals in extreme temperature conditions. Standard compounds handle operating temperatures -85º to +400ºF. Silicone compounds are popular in food and medical applications because they are clean and do not impart odor or taste. Special Phenyl silicones can be used down to -148°F.
13Other O-ring Materials Neoprene® / CR: Neoprene (-40º to +250ºF) features good resistance to petroleum oils, ozone, sunlight, relatively low compression set, good resilience and physical toughness. It is the preferred sealing material for the refrigeration industry because of its resistance to ammonia and Freon
31General Design Guidelines Stretch should be less than 5% on the O-ring I.D.Groove depth must be smaller than the O-ring CSO-ring should not completely fill the glandBetween 75% and 90%Static seal CS should be compressed from 10% to 40%Dynamic seals should be compressed from 10% to 30%
47The O-ring’s O. D. is larger than the cylinder bore diameter The O-ring’s O.D. is larger than the cylinder bore diameter. Peripheral squeeze is applied to the O.D. as the O-ring is installed into the bore. Incoming air pressure forces the O-ring against the walls sealing
48Floating O-Rings Advantage Limitations Greatly reduced breakout frictionLonger seal lifeLimitationsAir pressure less than 200 psi in pneumatic cylindersIn hydraulic systems small amount of leakage must be permissibleFloating O-rings are NOT suitable as rod seals
49Alternatives to O-Rings U-cup Seals O-rings have a tendency to roll and move in reciprocating motionsU-cups create more sealing as the pressure increasesU-cups require less precision for the associated hardware
54Due to centrifugal force and Gough-Joule effect rotary O-rings are only installed in the housing not on the shaft
55Gough-Joule effectWhen an elastomer is stretched and heated, it will contract.
56Rotary O-Ring Limitations O-ring seals are NOT recommended for rotary applications under the following conditions:Pressures exceeding 900 psiTemperatures lower than -40° F or higher than 225° FSurface speeds exceeding 600 feet per minute (fpm).2300 rpm for 1 inch diameter shaft1150 rpm for 2 inch diameter shaft
58Lip SealsLip seals work well in high speed low pressure rotating shafts
59Main Application of Lip Seals Ball and roller bearing protectionAs little as 0.002% water in lubrication oil can reduce ball bearing life by 50%Solid particles cause rapid damage to the bearing races.
62The purpose of the spring is to provide a uniform load on the lip The spring keeps the seal lip in contact with the shaft during higher speeds and also overcomes compression set and wear of the lip material.
63There is a tendency for liquids to be pumped from the low angle side towards the high angle side. Underneath the flattened area a thin fluid film is formed. Its thickness must be between 1 and 3 µm to avoid leakage
68Lip Seals To minimize wear The contact pressure should be as low as possible.Shaft surface should be smooth to µm.There must be enough fluid to form a hydrodynamic filmFluid pressure must be low (0-3 psi )
81Combustion Engine Piston Rings First compression ring (1)Second compression ring (2)Oil scraper ring (3)
82Piston Rings Compression ring Wiper ring (secondary compression ring) Seals the gases in the cylinderGas pressure forces the ring against the cylinder wallWiper ring (secondary compression ring)Seals the gases that escape the compression ringWipes excess oil from cylinder wallOil ringMade of two thin rails with slotsWipes excess oil from cylinder walls through port holes